Priority is claimed under 35 U.S.C. § 119(a) to Korean Patent Application No. 2004-103537 filed on Dec. 9, 2004, which is herein incorporated by reference.
1. Field of the Invention
The present invention relates to a method for fabricating an organic thin film transistor, and more particularly to a method for fabricating an organic thin film transistor comprising a gate electrode, a gate insulating film, source/drain electrodes and an organic semiconductor layer formed in this order on a substrate wherein the surface of the gate insulating film on which source/drain electrodes are formed is impregnated with an inorganic or organic acid, followed by annealing.
2. Descriotion of the Related Art
Since polyacetylenes as conjugated organic polymers exhibiting semiconductor characteristics were developed, organic semiconductors have been actively investigated as novel electrical and electronic materials in a wide variety of applications, e.g., functional electronic and optical devices, in terms of various manufacturing processes, easy molding into fibers and films, superior flexibility, high conductivity and low manufacturing costs.
Among devices fabricated by using these electrically conductive polymers, research on organic thin film transistors fabricated using organic materials as active layers has been conducted since 1980. In this connection, a number of studies are now being actively undertaken around the world. Organic thin film transistors are substantially identical to silicon (Si) thin film transistors in terms of their structure, but have a difference in that organic materials are used as materials for semiconductor regions instead of silicon (Si). In addition, such organic thin film transistors have the advantages that they can be fabricated by using printing processes at ambient pressure, instead of conventional silicon processes, such as plasma-enhanced chemical vapor deposition (CVD).
Organic thin film transistors are expected to be useful for driving devices of active displays and plastic chips for use in smart cards and inventory tags, and are comparable to α-Si thin film transistors in terms of their performance.
On the other hand, general organic thin film transistors (OTFTs) comprise a substrate, a gate electrode, a gate insulating film, source/drain electrodes, and an organic semiconductor layer. Organic thin film transistors can be classified into bottom-contact OTFTs wherein an organic semiconductor layer is formed on source/drain electrodes, and top-contact OTFTs wherein source-drain electrodes are formed on an organic semiconductor layer by mask deposition.
The fabrication of bottom-contact OTFTs involves a photoresist process for forming a pattern after deposition in order to form source-drain electrodes on a gate insulating film. At this time, the gate insulating film is exposed to a photoresist stripper and nitrogen generated from the stripper is adsorbed to the surface of the gate insulating film, leading to damage to the gate insulating film and thus making it impossible to fabricate OTFTs with superior insulating properties.
There have been introduced some attempts to reduce the damage to the surface of a gate insulating film. For example, damaged surface of a gate insulating film is physically treated using non-reactive gas plasma, or a gate insulating film is formed into a double layer by a self-assembly monolayer (SAM).
The aforementioned attempts simply smooth the damaged surface of the gate insulating film in a physical manner or necessitate an additional material for the formation of the double layer.